Tubes or pipes are often used to transport various fluids to or from various components within different systems. Tubes or pipes are often constructed from rigid, but smooth materials. Tubes or pipes are designed to be rigid to avoid failure or breaking of a tube, but designed to be internally smooth to allow for fluid to be transported through the tubes with minimal pressure loss. Although tubes and pipes are designed to be strong to avoid failure, they are also often manufactured with a thin wall thickness. This practice saves manufacturing costs and decreases the weight of the tubes. For example, the weight decrease may increase system efficiency when a tube is a component within a movable system, such as an automobile or aircraft.
Tubes may be used to carry high pressure fluids such as oil, gas, air, or water. When the tubes carry flammable substances, such as oil or gas, safety is a concern. More specifically, leaks of flammable fluids caused by pipe or tube failures, or failed connections between tubes or pipes and fittings, are a major safety concern. One solution to this problem is to use double-wall tubes or pipes. A double wall pipe or tube is simply a secondary tube surrounding a primary tube. In some instances flow is designed to flow in both tubes. In other instances, flow is designed to flow in the primary (inner) tube and the secondary (outer) tube is designed to prevent leakage. The latter of these instances provides safety and redundancy required in aviation.